Expansion plugs with an anchor bolt, an expansion element, force-applying means as well as an expansion sleeve surrounding the anchor bolt serve to fasten workpieces to a structure. For this purpose, a hole is drilled into the structure, for example, a concrete wall or a concrete floor, and then the expansion plug is pushed into the drilled hole. The force-applying means move the conical expansion element axially on the anchor bolt, so that as a result, the expansion element presses the expansion sleeve radially outwards and the expansion plug is anchored due to the radial forces between the expansion sleeve or the expansion element and the structure, for example, the concrete surrounding the drilled hole. In this manner, workpieces or objects can be fastened to the expansion plug.
Therefore, a frictional force between the wall of the drilled hole and the expansion sleeve anchors the expansion plug between the expansion sleeve and the wall of the hole drilled into the structure. The conical expansion elements are generally rotation-symmetrical to a longitudinal axis of the anchor bolt or of the expansion element.
For instance, a thread on the anchor bolt, a washer and a nut are used as the force-applying means. When the nut is screwed onto the thread of the anchor bolt, the washer is pressed against the concrete at the mouth of the drilled hole, thereby causing an axial movement of the anchor bolt and thus also of the conical expansion element. Thus, a torque has to be applied to the nut in order to screw it onto the thread on the anchor bolt or in order to screw it in. When the expansion plug is used in pulling zones, that is to say, in the case of cracked concrete in prestressed concrete in which small cracks appear at the bottom of the prestressed concrete floor, the diameter of the drilled hole becomes larger during the expansion of the expansion sleeve with the expansion element. This results in an additional axial movement of the anchor bolt with the expansion sleeve, the so-called post-expansion, during the radial tensioning of the expansion sleeve on the concrete surrounding the drilled hole. The expansion element, that is to say, here especially the conical geometry of the expansion element, has to be configured in such a way that the requisite expansion force, i.e. the radial pre-tensioning between the expansion sleeve and the concrete surrounding the drilled hole, can be achieved in a lower tolerance range of the drilled hole diameter as well as in an upper tolerance range of the drilled hole diameter. Depending on the varying diameters of the drilled hole within the tolerance range, this leads to different axial movement paths between the anchor bolt and the expansion sleeve. In the case of drilled hole diameters in the upper tolerance range, the expansion sleeve can additionally move relative to the drilled hole (sleeve slippage). In the case of sleeve slippage, the various anchor bolts protrude to a different extent out of the drilled hole when a differing sleeve slippage occurs, and an axial movement of the expansion sleeve towards the mouth of the drilled hole also results in detrimental different anchoring depths of the expansion plug in the drilled hole. The consequence is a greater spread of the breaking load of the expansion plugs.
German patent application DE 41 16 149 A1 describes an expansion plug with an anchor bolt whose cylindrical shank has a widening in the setting direction in one end area and which, for purposes of bearing a load, has force-applying means on the end facing away from this widening, whereby the anchor bolt, at least along part of its shank, is surrounded by an expansion sleeve that can be moved relative thereto, that has at least one lengthwise slit open towards the end on the setting side, and that is provided with radially extending projections on its outer contour.